Building a “System”

1. Building a “System” • Moving from writing a program to building a system. What’s the difference?! • Complexity, size, Complexity, size ------ Complexity Breadth of Complexity Depth of Complexity

2. Increase of Complexity Everywhere Solution Problem transformation Increase in effort due to size & complexity Increase in size & complexity Increase in size & complexity

3. Complexity (Breadth) • More Functionalities • More Features within each functionality • More varieties of Interfaces (internal & external) • More Users and varieties of users • More data, varieties of data, data structures For your assignment 1, what happens if the number of input data increases to 1 trillion and the input numbers themselves are pretty large ?

4. Complexity (Depth) • More Linkages and Connections • Data sharing among the functionalities & logic • Control Passing among functionalities

5. Examples for in-class Discussion • Assignment 1 ---- compute and show the “average” of the read-in numbers • “Modified” Assignment 1 ---- show the largest and the smallest of the read-in numbers • Where is the complexity increase? • “Further Modified” Assignment 1 ---- show the read-in numbers in a sorted ascending order. • Where is the complexity increase?

6. Handling Complexities(A) • Via “Simplification” • Decompositionof the problem and of the solution • Modularizationof solution • Separation of Concernsof problem and of solution • Incrementally resolve problems *** Not “advertised” but a sometimes used technique is: REDUCEthe problem

7. Handling Complexities(B) • Via “Improving Technology and Tools” • Database to handle information and structures of information • Programming & Dev. Platforms • Computing Network • Multi-Developer Configuration Management • Modeling techniques of problem and solution • Automated Testing Note: the first time you use these, it will actually be more complex

8. Handling Complexities(C) • Via “Improving Process and Methodologies” • Coordinate multiple and different people performing different tasks • Guidance for overlapping incremental tasks • Guidance for measuring separate artifacts and outcomes Note: first time you put in a process --- it is like the new tool - - - it is more complex.

9. Example of Size and Complexity Increases (b)Increased Size and Complexity (a)Simple Start Start Wait for signal Perform task A Signal is? Perform task B ‘a’ other ‘b’ Perform task A Perform task C Perform task C Perform task A2 Perform task B Stop Stop

10. Task Breakdown (Macro) Example (Handling Complexity) Requirements Definition Support & Problem Fixes Code/Unit Test Design Integration & System Test 1. Who performs what task? 2. How is the task completed with what technique or tool? 3. When should which task start and end? 4. Who should coordinate the people and the tasks?

11. Iterative Process Example (Handling Complexity) Understanding the Broad Problem (Req.) Architecture and High Level Design Specific Requirements Specific Requirements . . . . Detail design . . . . Detail design Code . . . . Code Integration Test / Fix Test / Fix

12. Handling the “Details” separately Integration • Seemingly “simple” Test/Fix and Integrate steps: • Should there be separate & independent test group? • How should problem be reported and to whom? • How much information must accompany a problem report? • Who decides on the priority of the problem? • How is the problem fix returned? • Should all problems be fixed? • What should we do with non-fixed problem? • How are fixes integrated back to the system? Test / Fix Test / Fix

13. Some ‘Non-technical’ Considerations for Developing & Supporting a System (requiring more effort, more resources, etc.) • Effort & Schedule Expansion • How does one estimate and handle this? • Assignment and Communications Expansion? • Do we need some process? • Do we need some tools?

14. Increase in Amount of Communications as # of People Increases. Also, an increase in the number of communications errors committed With the increase in system complexity, there is a corresponding increase in the “manpower” or human resources. 4 people: possibly 6 paths 6 people: increase to potentially 15 paths 2 people: 1 path For n people, number of potential communications paths = ∑ (n-1) = [nx(n-1)] / 2

15. A Large, Complex System • Building “Mission critical” or “Business critical” system (e.g. payroll - in textbook) requires (1)several separate activities performed by (2)more than 1 person (e.g. 50 ~ 100): • Requirements: gathering, analysis, specification, and agreement • Design: abstraction, decomposition, cohesion, interaction and coupling analysis • Implementation: coding and unit testing • Integration and tracking of pieces and parts • Separate testing: functional testing, component testing, system testing, and performance testing • Packaging and releasing the system

16. Also, Need to ‘Support’ the “Payroll” System in text (for real production)(often times complex systems are not “perfect” ) • Pre-release: preparation for education & support: • Number of expected users • Number of “known problems” and expected quality • Amount of user and support personnel training • number of fix and maintenance cycle • Post-release:preparation foruser and customer support: • Call center and problem resolutions • Major problem fixes and code changes • Functional modifications and enhancements

17. CoordinationEfforts Required in Systems Development and Support • Because there are i) more parts, ii) more developers and iii) more users to consider in “Large Systems” than a single program developed by a single person for a limited number of users, there is the need for Coordination of (3P’s): • ‘Processes’ and methodologies to be used • Final ‘product’ and intermediate artifacts • ‘People’ (developers, support personnel, and users) The previous diagram on people increase and potential communication paths increase provides a clue to the importance of coordination efforts.